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Pressure + GPM

My static pressure at the closest hose bib to my meter (in house) is 50 psi. Using the toro psi/gpm manifold set, i only get 3.4 - 4 gpm at 35 psi witch i know is low. My home supply after the meter is 3/4" copper, and the hose bib outside i know is 1/2". Is there a formula or table to tell me what my gpm would be off of 3/4" or is there a big difference?!? Can I turn up my water regulator (max setting of 80 psi) to get a better working pressure or gpm?!?

Also, is it better to run 1" poly after the valves, or should i keep it 3/4"?!?

I think this is going to be close. Take the diameter of your pipe hose bib and use that to calculate the area of the pipe. Pie* radius squared= area of a circle. so .5*.5*3.14=.785 then do the same for your house main .75*.75*3.14=1.76 because the flow is directly related to the size of the pipe we take thes 2 numbers and divide 1.76/.785= 2.25 This says a 3/4 inch pipe will allow 2.25 more flow than a half inch pipe. Now take 3.4 *2.25=7.65 gpm. I used the 3.4 number to esimate conservatively.

wouldn't the gpm for 3/4 pipe be 5.65 (3.4 gpm from 1/2" + 2.25 gpm upgrading to 3/4" using the formula)?!? Am I correct in assuming that the pressure would be the same reguardless of pipe size (1/2" or 3/4")?!? If I got 40psi on 1/2, it would be 40psi on 3/4? Thanks for all the help!!

If your meter is 5/8" and your supply is 3/4" you should be able to design for 10 gpm. Also, make sure your valves before and after the meter are fully open. Many times, I find these valves to be partially closed.

I too have used the Toro 53351 flow/pressure meter and found it to be way off from the 5 gal bucket calculation method, (I am still trying to find someone who can explain that). To get a good idea of your flow at the design pressure, attach a hose to the hose bib near the meter inside the house. Run the water from there into a drain or sump crock and bring the flow up until the pressure stays constant at or above the design pressure (You may have to fasion a few fitings and a gauge to messure the pressure while you do this if there is not already one in place). Once the pressure stays constant for several minutes, fill a 5 gal bucket and measure the time to do so. You may want to do this several times and take the average number. Then complete this calculation, 60secs / secs to fill 5 gals x 5 = gallon per minut of flow. Be sure that you know the point at which your bucket measures 5 gals as many actually hold more than that.

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by SprinklerHead</i>
<br />I too have used the Toro 53351 flow/pressure meter and found it to be way off from the 5 gal bucket calculation method, (I am still trying to find someone who can explain that). To get a good idea of your flow at the design pressure, attach a hose to the hose bib near the meter inside the house. Run the water from there into a drain or sump crock and bring the flow up until the pressure stays constant at or above the design pressure (You may have to fasion a few fitings and a gauge to messure the pressure while you do this if there is not already one in place). Once the pressure stays constant for several minutes, fill a 5 gal bucket and measure the time to do so. You may want to do this several times and take the average number. Then complete this calculation, 60secs / secs to fill 5 gals x 5 = gallon per minut of flow. Be sure that you know the point at which your bucket measures 5 gals as many actually hold more than that.
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I am desiging am irrigation system for a house in Italy. There are many challanges, including the fact that the water supply is a well. I had thought to measure the capacity using the Toro 53351, but maybe not... I would still like to try this method, does anybody have one they would like to sell?

pressure is the same no matter what size pipe. gpm is better the larger the pipe. your 3/4 inch service will provide about 6-8 gpm. thats why you tap of that and not half inch. psi and flow(gpm) go hand in hand. the 5 gallon bucket test for flow is a good method. to be safe, tap off your 3/4 inch service and dont exceed 6 gpm. if it is going to make too many zones that way, get a booster pump. booster pumps are very tricky and difficult for the average homeowner to install properly. a pro may be needed unless you know plumbing and electrical very well. but it will make a BIG difference.